Embodiments relate generally to the field of marine geophysical surveying and, more particularly, embodiments relate to methods and systems for mitigating noise and the effect of linear acceleration in orientation sensors used with geophysical surveying equipment.
Techniques for marine geophysical surveying include seismic surveying and electromagnetic surveying, in which geophysical data may be collected from below the Earth's surface. Marine geophysical surveying has applications in mineral and energy exploration and production and may be used to help identify locations of hydrocarbon-bearing formations. Certain types of marine geophysical surveying, including seismic and electromagnetic surveying, may include using a survey vessel to tow an energy source at selected depths—typically above the seafloor—in a body of water. One or more streamers may also be towed in the water at the selected depths by the same or a different survey vessel. The streamers are typically cables that include a plurality of geophysical sensors disposed thereon at spaced apart locations along the length of the cable. Some geophysical surveys locate the geophysical sensors on ocean bottom cables or nodes in addition to, or instead of, streamers. The geophysical sensors may be configured to generate a signal that is related to a parameter being measured by the geophysical sensor. At selected times, the energy source may be actuated to generate, for example, seismic or electromagnetic energy that travels downwardly into the subsurface formation. Energy that interacts with interfaces, generally at the boundaries between layers of subsurface formations, may be returned toward the surface and detected by the geophysical sensors on the streamers. The detected energy may be used to infer certain properties of the subsurface formation, such as structure, mineral composition and fluid content, thereby providing information useful in the recovery of hydrocarbons.
Some geophysical surveying techniques may use orientation sensors with the geophysical surveying equipment (e.g., streamers, sensors, ocean bottom cables, sources, paravanes, etc.). Orientation sensors, such as a tilt sensor and/or a roll sensor, may be used to determine an orientation of the geophysical surveying equipment. For example, an orientation sensor may be used to determine the orientation of a non-gimbaled AC-coupled motion sensor, such as a piezoelectric accelerometer with a fixed mount. A typical orientation sensor used with geophysical surveying equipment may be a DC-coupled accelerometer, such as a micro-electromechanical system (MEMS) accelerometer. However, there may be locations along the geophysical surveying equipment where the level of overlaid linear acceleration may make an accurate orientation determination difficult (e.g., at the head end of a streamer). Therefore it may be desirable to find a complimentary orientation sensor that can measure orientation without being affected by overlaid linear acceleration or vibration.